Restrictions of cervical flexion after laminoplasty increase in the mechanical stress at the occipitocervical junction in non-rheumatoid arthritis patients.

Increased range of motion (ROM) at O-C2 after cervical laminoplasty is thought to be a compensatory change due to loss of cervical ROM after surgery. Retro-odontoid pseudotumor in non-RA patients is also caused by loss of ROM at C2-C7 causing mechanical stress on upper cervical spine. The aim of this study was to measure the occipitocervical alignment before and after cervical laminoplasty, and examine the factors associated with postoperative retro-odontoid soft tissue (ROST) enlargement. The study comprised 72 non-RA patients (51 males and 21 females, mean age 65.2years) who underwent cervical laminoplasty. The cervical angles (O-C1, O-C2, C1-C2, and C2-C7) were measured and ROST thickness was evaluated on mid-sagittal T1-weighted MRI before surgery and 2years after surgery. Correlations between radiographic changes and postoperative ROST enlargement were examined. The results shows that postoperative ROM and kyphotic angle in flexion position at O-C2 significantly increased, and postoperative ROM and kyphotic angle in flexion position at C2-C7 significantly decreased compared with preoperative values. On stepwise multiple regression analysis, age (beta=0.273, p<0.01) and restriction of cervical flexion postoperatively (beta=0.235, p<0.01) were independently associated with ROST enlargement. In conclusion, occipitocervical ROM increased and C2-C7 ROM, especially C2-C7 kyphotic angle in flexion, reduced after cervical laminoplasty. The ROST enlargement was associated with reduction in cervical flexion. These results indicate that preservation of cervical ROM, especially kyphotic angle in flexion, after cervical laminoplasty contribute to reduction of mechanical stress at the occipitocervical junction.